RF signals are measured and processed for a variety of purposes. For example, RF signals are measured and processed when designing and testing RF devices, such as cellular telephones, RF test equipment, and VHF transceivers. Signal power, modulation, harmonic distortion, and noise are examples of different measurements that are measured for an RF device. The measurements may then be displayed to a user in a graph that plots the measurement over time or frequency.
FIG. 1 is a flowchart of a method for displaying signal envelope information in accordance with the prior art. Signal envelope information typically displays RF signal characteristics in terms of a measured value, such as power, with respect to time. Initially RF data values are sampled and converted to baseband or intermediate frequency (IF) data. The IF data values are converted, for example, to in-phase (I) and quadrature (Q) complex data pairs. The complex data are then stored, as shown in block 100.
A determination is then made at block 102 as to whether more complex data pairs are to be acquired and stored. If so, the process returns to block 100. When all of the data have been acquired and stored, the method passes to block 104 where the block of complex data is processed. The complex data values are processed for a particular application. To display signal power envelope information, for example, the log of the magnitude (√{square root over (I2+Q2)}) for each complex data pair is calculated. The results are then displayed, as shown in block 106.
The speed at which the data values are processed and the graphs or displays of the signal information (e.g., envelope, overview) are output to a monitor can be impacted in the method of FIG. 1. Post-processing of the complex data pairs can be time-consuming, especially when large amounts of sampled data have been acquired. Moreover, the types of calculations performed with the stored data values can also impact the speed. Calculations on complex data, such as log (√{square root over (I2+Q2)}), can significantly reduce the speed of the data processing when performed post acquisition. Typically many of the display formats require some trigonometric or other computationally expensive function. For large data captures of complex time data, a viewer can wait a long period of time before the signal envelope calculation or some other calculation is displayed. To reduce this waiting period, some systems decimate or re-sample the data prior to performing the computations in order to reduce the amount of data that is processed. For example, some systems discard N−1 of N values. But this can result in the loss of significant information.